Converter polarizing system



C. P WEST CONVERTER POLAHIZING SYSTEM March 22, 1932. Re. 18,391

0 ginal Filed June 16., 1928 II I INVENTOR Charles P. wes f AT'iORNEYReissued Mar. 22, 1932 UNITED STATES CHARLES P. WEST, OF EDGE-WOOD,PENNSYLVANIA, ASSIG-NOR TO WESTINGHOUSE ELEC- TRIC & MANUFACTURINGCOMPANY, A CORPORATION OF PENNSYLVANIA CONVERTER POLARIZIN G SYSTEMOriginal No. 1,763,622, dated June 10, 1930, Serial No.

filed May 25, 1931.

My invention relates to automatic sub-stations and, more particularly,to sub-stations of the type in which a synchronous rotary converter isadapted to" be started automatically in response to differentconditions, and connected to a direct-current load circuit.

One object of my invention is to provide means for insuring that anormally self-eX- cited rotary converter in an automatic station willdevelop a predetermined polarity at its direct-current brushes.

Another object of my invention is to provide means for starting asynchronous converter on reduced voltage and automatically transferringit to a. source of normal voltage when it accelerates to synchronousspeed and develops a predetermined polarity at its direct-currentbrushes.

A further object of my invention is to pro vide means for so biasing theconverter excitation that the machine will always develop the samepolarity at its direct-current terminals.

A still further object of this invention is the provision of a startingsystem for a rotary converter in which the converter field ispermanently connected in shunt to a resistor and in series with theconverter brushes and during the staring period, in series with auni-directional current-conducting device.

A still further object of this invention is the provision of a startingsystem for converters in which the shunt field is energized by one setof half-cycles of the alternating voltage which appears at thedirect-current brushes during starting and also by a separate source ofdirect current during the start ing period. a

In accordance with my invention, I provide means for applying a reducedvoltage to the armature of a synchronous converter. I connect the shuntfield winding of the converter permanently to a resistor ofcomparatively high resistance. The shunt field winding is also connectedacross the direct-current brushes of the converter, and during starting,in series with a uni-directional currentconducting device. The shuntfield winding is also connected to a separate source of direct current.By these means, the shunt field 286,021, filed June 16, 1928.Application for reissue Serial No. 539,954.

winding of the converter is always energized by current in a givendirection during the starting period, and the converter develops apredetermined polarity at the direct-current brushes every time it isstarted.

I provide also, means for controlling the transfer of the converterarmature from starting to running voltage. This means is responsive tothe development of a definite polarity at the direct-current brushes ofthe converter.

The details of the system of my invention will be described hereinafter,and the novel features thereof will be pointed out in the appendedclaims. For a complete understanding of my invention, the accompanyingdrawing should be referred to in connection with the followingdescription.

7 The single figure of the drawing is a diagrammatic illustration of thecircuits and apparatus necessary for a satisfactory functioning of myinvention.

Referring in detail to the drawing, a polyphase alternating-currentsource is indicated at 10. Transformers 11 have their primary windingsconnected to the source 10, while their secondaries are adapted to beconnected to the slip rings of a synchronous converter 12.

The connection of the converter 12 to the secondaries of thetransformers 11 is controlled by'a starting switch 13 which connects thelow-voltage taps of the transformer tothe slip rings and a runningswitch 14., which, when closed, supplied full voltage from thetransformers to the converter.

The converter field is indicated at 15 and is permanently shunted by a.high-resistance shunt 16, and, at the same time, is connected across theconverter brushes in series with a rheostat 17 a field-ki1lingresistance 18 and a uni-directional current-conducting device 19. Thislast mentioned device is pref. erably a copper-oxide disc rectifier,although any other equivalent means may be substituted. The function ofthe resistor 18 is to reduce the converter excitation when the machineis disconnected from the circuit 10 to prevent it from coasting as asynchronous generator.

Auxiliary relays 20 and 21 are employed to control the operation of thestarting and running switches and are, in turn, controlled by additionalauxiliary relays 22 and 23, in a manner to be described in detailhereinafter.

A full-wave rectifier 24, which is also preferably of the copper-oxidedisc type, is adapted to be energized by the transformer 25 connected tothe secondary of one of the transformers 11. The direct-currentterminals of the rectifier 24 are adapted to be connected to theterminals of the field winding 15, during the starting period.

To control the transfer of the converter armature from starting torunning voltage, I make use of an iron-core reactor 26. This reactor hasan alternating-current winding 27 connected to a source ofalternating-current, such as a transformer 28, and to the winding of therelay 23. The reactor also has a directcurrent winding 29 and a closedcircuit winding 30.

The iron-core reactor serves as a control device and its operation isbased upon the well-known principle that the super-position of auni-directional flux upon an alternating flux in a magnetic circuit hasthe effect of reducing the impedance of the winding inducing thealternating flux. In the specific embodiment of my invention described,the impedance of the alternating-current winding 27 is high, as long asthe direct-current winding 29 is substantially de-energized. When thewinding 29 is energized, however, the impedance of thealternating-current winding 27 is decreased to a minimum. 7

The remaining features of my invention will be pointed out in connectionwith the following description of operation.

Energy for the operation of the control devices involved in my inventionmay be taken from control buses31 and 32, which may be energized fromany convenient current source. In order to initiate the operation of thesystem of my invention, it is only necessary to close the'switches 33,which connect the control buses 31 and 32 to their source of supply, andthe switch 34 which completes the circuit from the transformer 25 to therectifier 24. The switches 33 and 34 may be closed by any suitableautomatic means although for simplicity, they are here shown as manualswitches.

Upon the closure of switch 34, a circuit is completed from thetransformer 25 through the rectifier 24 and a normally closed switch 35actuated by the running switch 14.

A circuit is completed by the closure of switch 33 for the operatingcoil of the relay 20, from the control bus 31, through a .normallyclosed switch 36 of the relay 22, to the coil of the relay 20 and thusto the bus 32. The energization of the coil of relay 20 results in theclosure of its normally open switches 37, 38 and 39. The closure of theswitch 37 completes a circuit from the control bus 31, through theoperating coil of the starting switch 13 and the switch 37 to the bus32.

As a result of the completion of the justmentioned circuit, the startingswitch 13 is closed, and low voltage is applied to the slip rings of theconverter which startsto rotate in the well known manner, the fieldwinding of the converter being shunted through the high resistance 16.During the starting operation, an alternating current is induced in thecircuit including the field winding 15 and the resistor 16. The fieldwinding is shunted to prevent the occurrence of high voltages in thefield circuit. 1

The closing of the switch 38 of the relay 20 connects the direct-currentterminals of the rectifier 24 to the field winding 15, and the closingof the switch 39 short circuits the rheostat 17 and the resistor 18 inthe field circuit.

During the starting period, in addition to the alternating currentinduced in the field winding which flows through the resistor 16,alternating current is also supplied to the field circuit from theconverter brushes. This alternating current, however, is rectified bythe rectifier 19 so that the converter field is energized only by thepositive half-cycles of the alternating current from the converterbrushes. The rectifier 24 also supplies direct current to the fieldwinding 15 in the same direction as that which flows as a result of thealternating voltage at the converter brushes.

Thus, the field current which flows during the starting operationconsists of three components, first, that which flows through theresistor 16; because of the alternating voltage induced in the fieldwinding itself, second, that due to the alternating voltage on theconverter brushes which is rectified and flows only in one directionthrough the field winding 15, and, third, the direct current suppliedfrom the rectifier 24 to the field winding 15. The system of myinvention obviously may be so designed and arranged that the effect ofthe direct-current components of the field current are suflicient toovercome the eifect of the alternating current flowing in the circuitcomposed of the winding 15 and the resistor 16. v

It wiuld be a simple matter to rectify the current in the lattercircuit, but, as already stated, thiscurrent is permitted to circulatein the circuit 1516 to prevent the abnormal voltages that wouldotherwise be induced therein, and the direct-current components of thefield current are relied upon to bias the converter excitation so thatthe machine will accelerate-to synchronous speed with a defi+ nitepolarity at the direct-current brushes. By supplying suflicient directcurrentto nullify the effect of the negative half-cycles of the inducedalternating current, it is possible to insure that the polarity of thedirect-current brushes will always be the same.

It will be observed that the so-called direct-current winding 29 of thereactor 26 is connected across the converter brushes in series with aresistor 40 and a single-wave rectifier 41. This circuit is subject toalternating voltage of decreasing frequency which appears at theconverter brushes as the converter accelerates to synchronous speed. Therectifier 41, however, prevents the negative half-cycle of thisalternating current from flowing, and the winding 29 is energized,therefore, by a substantially constant direct current.

When the converter has accelerated to synchronous speed and developed apredetermined polarity at its direct-current brushes, the winding 29 ofthe reactor 26 will be sufficiently energized to substantially decreasethe impedance of the winding 27. As long as the converter is belowsynchronous speed, however, the positive half-cycles of the alternatingcurrent flowing in the circuit includ ing the winding 29, will beinsufficient to energize the winding 29, so that the impedance of thewinding 27 is substantially decreased. Vhen the impedance of the winding27 is reduced to a predetermined value, however, by the energization ofthe winding 29, the current supplied therethrough by the source 28 tothe winding of the relay 23 is suflicient to energize the latter tocause it to close its switch. The closed-circuit winding 30 functions tointroduce a time delay in the operation of the reactor 26, but is notessential and may be omitted if desired.

The closure of the switch of the relay 23 completes a circuit from thecontrol bus 31 through the switch 42, which was closed by the operationof the relay 13, through the switch 23, the operating coil of the relay22 and thence to the bus 32.

he energization of the operating coil of the relay 22 results in theopening of the switch .36 thereof and the closure of the switches 43 and44. The opening of the switch 36 interrupts the circuit including theoperating coil of the relay 20 which is thereupon de-energized to openthe switches 37, 38 and 39. The opening of the switch 37 interrupts thecircuit including the operating coil of the starting switch 13, whichthereupon opens, and, at the same time, closes its switch 45 and opensits switch 42. The opening of the switch 42 interrupts the originalenergizing circuit of the relay 22 but a looking circuit for theoperating coil of this relay is completed through its switch 43, whichis closed when the relay is first energized. The closing of the switch44 of the relay 22 short circuits field-killing resistor 18 and therectifier 19. The opening of the switch 38 of the relay 20 disconnectsthe field winding 15 from the rectifier 24, and the opening of theswitch 39 interrupts the circuit in shunt with the rheostat 17 and theresistor 18.

When the operations just described have been completed, a circuit isestablished for the operating coil of the relay 21, which extends fromthe control bus 31, through switch 43 of the relay 22, the switch 45 ofthe starting switch 13 and the operating coil of relay 21, to the bus32. The relay 21, upon being energized, closes its switch to complete acircuit from the control bus .31, through the operating coil of therunning switch 14 and the switch of the relay 21 to the control bus 32.

The running switch 14 is thereupon closed, and full voltage is appliedto the armature of the converter. At the same time, the switch 35 isopened by the operation of the switch 14, and the energizing circuit ofthe rectifier 24 is interrupted.

It will be observed that upon the completion of the operationsdescribed, the converter will be connected to a source of normal voltageand will be running at synchronous speed, and there will be a definitepredetermined polarity on the brushes of the converter. The connectionof the converter to its direct-current load circuit may be effected byany known system of automatic switching, which forms no part of myinvention.

The system of my invention may be uti lized in connection with means forlifting the brushes of the converter during starting or this feature maybe entirely omitted, according to the characteristics of the converterin question.

The details of the system of my invention may also be altered to suitthe circumstances of any installation. The rectifier 24, for eX- ample,may be replaced by any other convenient source of direct current. Thetransformer 28 may be connected to the same source as the powertransformers 11, or any other convenient source of alternating currentmay be employed instead. 7

It will be obvious that the system of my. invention insures that asynchronous converter, when automatically started, will always come intosynchronism with a predetermined polarity on the direct-current brushes.This feature is a. great advantage-over systems of the prior art, inwhich the converter was allowed to come into synchronism at random, andits polarity was then checked and altered if incorrect.

Another advantage of the system of my invention resides in the fact thatthe fieldwinding circuit is never opened, but is permanently connectedacross the converter brushes. Because of the considerable inductance ofthis circuit, any interruption in the flow of current therein isattended with destructive arcing which it is desirable to avoid. Thepresent system accomplishes this result.

I am aware that it has been common practice heretofore to flash thefield of a synchronous converter to predetermine its polarity, but Ibelieve I am the first to propose the use of a rectifier for suppressingthe negative half-cycles of the alternating current flowing through thefield winding from the converter brushes during the starting period inconnection with a separate source of exciting current for the fieldwinding.

. uni-directional As hereinbefore mentioned, changes may be made in thesystem of my invention, and I do not intend tobe limited to the specificmodification disclosed herein, except as necessitated by the appendedclaims and the state of the prior art.

I claim as my invention:

1. An automatic station comprising a rotary converter, provided with afield winding, a rectifier adapted to be connected in series with saidfield winding and the converter commutator during the starting of theconverter, means for applying reduced voltage to the converter armature,an independent source of direct current adapted to be temporarilyconnected to said field winding, a relay, an alternating-current source,an iron-core reactor having an alternatingcurrent winding connected inseries with said relay to said alternating-current source, adirect-current winding on said reactor connected to the convertercommutator for causing the operation of said relay, and switchescontrolled by said relay for transferring the converter armature fromlow voltage to normal voltage.

2. In an automatic stat-ion, a rotary converter, a resistor permanentlyshunted across the'shunt field winding of the converter, acurrent-conducting device adapted to be connected in series with thefield winding and the converter commutator, a separate source of directcurrent adapted to be temporarily connectedto said fieldwinding, meansfor applying a reduced volt-age to the armature, a relay for causing thearmature to be transferred to full voltage when the converter attainssynchronous speed and a definite polarity, control means for said relayincluding an iron-core reactor having an alternating-current windingconnected to an alternating-current source in series with said relay,and a direct-current winding connected across the converter commutator.

3. An automatic translating station comprising a rotary converter havingshunt field and armature windings, a rectifier adapted to be connectedin series with the field winding across the converter commutator, asecond rectifier for supplying direct current to said field windingduring starting, means for applying a reduced voltage to the converterarmature, a relay for transferring the armature to full voltage, avariable imped- I ance responsive to a uniform voltage across theconverter brushes for controlling the operation of said relay, wherebysaid transfer is efiected automatically when the converter reachessynchronous speed and attains a definite polarity, and means forshort-circuiting said first-mentioned rectifier and disconnecting saidsecond rectifier.

4. In an automatic station, the combination with a rotary converterhaving shunt field and armature windings, a rectifier adaptedto Y beconnected in series with the field winding across the convertercommutator, means for supplying reduced voltage to the armature to startthe converter, means for supplying direct current to the field winding,of means r for transferring the armature to full voltage including areactor having alternating-current and direct-current windings, thedirectcurrent winding being connected across the converter commutatorand a relay connected in series with said alternating-current wind- 5,The combination with a rotary converter having armature and shunt fieldwlndlngs,

a uni-directional current-conducting device 7 adapted to be connected inseries with said field winding across the converter commutator, anindependent source of direct current adapted to be temporarily connectedto said field winding, of means for controlling the transfer of theconverter armature to full voltage including a relay and a variableimpedance connected in series therewith, and means effective when theconverter attains synchronous speed and a definite polarity for reducingsaid impedance to operate said relay.

6. In an automatic station, a rotary converter having shunt field andarmature windings, the field winding being connected permanently acrossthe converter commutator, means for applying a reduced voltage to saidarmature winding to start the converter, means for preventing the fiowof current in one direction through the field in response shunt fieldwinding across the converter commutator, means for starting theconverter on reduced voltage, means for limiting the flow of current inthe field in response to the alternating voltage on the convertercommutator to one direction only, means for supplying current to saidfield winding in said direction, and means for limiting the fiow ofalternating current in said field winding in response to the alternatingvoltage induced therein during starting.

8. In an automatic station, the combination with a rotary converter,having a shunt field winding permanently connected across the convertercommutator, means for starting the converter on reduced voltage, meansfor energizing the field winding of the converter with direct current,means for preventing the flow of current in one direction through saidfield as a result of the alternating voltage on the convertercommutator, and means responsive to a definite polarity on saidcommutator for eifecting the transfer of the converter armature to asource of normal volt-age.

9. A starting system for a synchronous converter including means forapplying reduced voltage to the converter armature to start theconverter, means for limiting the flow of current to the field windingfrom the converter commutator during starting to one direction, andmeans responsive to a uniform voltage of definite polarity on saidcommutator for transferring the converter armature to a source of normalrunning voltage.

10. A starting system for synchronous con verters including means forpreventing flow of current in one direction to the converter fieldwinding from the commutator of the converter during starting, and means,including an iron-core reactor, for transferring the converter fromstarting to running voltage when a uniform voltage of definite polarityexists on said commutator.

11. A starting system for synchronous converters comprising means forapplying a reduced voltage to the converter armature and means includingan iron-core reactor having direct-current and alternating-currentwindings responsive to the existence of a uniform voltage of definitepolarity on the converter commutator for transferring the converterarmature from a reduced voltage to full voltage.

12. In an automatic station, a power translating device havingalternating-current and direct-current terminals and an excitingwinding, a power source, means for connecting the power translatingdevice to the power source, means for connecting the exciting winding to'the direct-current terminals, means for limiting the flow of generatedcurrent in the exciting winding to a predetermined direction only, andmeans for supplying uni-directional current to the exciting winding insaid predetermined direction during the starting period, whereby thepower translating device is caused to develop a predetermined polarityat the direct-current terminal when starting.

13. In a starting system for a rotary converter having shunt field andarmature windings, in combination, a source of power for the converter,means for connecting the converter to the power source, means forconnecting the shunt field winding across the converter armature, meansfor causing the generated current in the shunt field circuit to flow inone direction only, and means fol simultaneously supplying additionaluni-directional excitation current to the field winding in. saiddirection, thereby to cause the converter. to develop a predeterminedpolarity each time it is started.

14. In a'starting system for a rotary converter provided [with field andarmature windings, said field winding being connected across thecommutator of the converter, a source of power, means for connecting theconverter to the power source, means comprising a rectifier for causingthe generated current in the field circuit to flow in one direction onlyduring the starting period, and lneans for supplying additionalunidirecs tional current in said one direction to the field winding fromthe source of power durlng the starting period, thereby, to insure thatthe polarity of the converter will build upin a predetermined direction.

15. In an automatic station, in combination, a rotary converter havingshunt field and armature windings, said field winding being connectedacross the commutatorof the converter, a source of power, means forstarting the converter on reduced voltage, means in the field circuitfor controlling the direction of the flow of current in the fieldwinding caused by the alternating voltage on the commutator, and meansincluding a rectifier for supplying unidirectional current to the fieldin the same direction as the current supplied from the commutator,thereby to insure that the polarity of the converter will always buildup in a predetermined direction.

16. In an automatic station, in combination, a rotary converter havingshunt field and armature windings, said field winding being connectedacross the commutator of the converter, a source of power, means forstarting the converter on reduced voltage, rectifier means connected inseries-circuit relation with the field winding disposed to cause thealternating current from the converter armature during starting to flowonly in a predetermined direction, and means for continuously excitingthe field windings with unidirectional current in said predetermineddirection from the power source during the starting period, whereby theconverter is always caused to develop a predetermined polarity when itreaches synchronous speed.

17 In a starting system for a synchronous converter having a shunt fieldwinding, in combination, a source of alternating-current power for theconverter, means for supplying reduced voltagefrom the power source 1 tostart the converter, a rectifier connected in series with the shuntfield winding to cause the alternating current from the convertercommutator to flow only in a predetermined direction, an independentsource of direct current connected to the field winding to excite thefield winding with unidirectional current in said predetermineddirection to cause the converter to develop a predetermined polarity,and meansfor connecting the converter directly to the power source whenthe converter attains substantially synchronous speed and for renderingthe rectifier and the independent source of direct current ineffectiveto further influence the excitation of the converter.

18. In a control system, in combination, a rotary converter providedwith armature and field windings and a commutator, said field windingbeing connected across the commutator, means for starting the converteron reduced voltage, a rectifier device connected in the field circuit todirect the flow of current from the commutator in a predetermineddirection only when the converter is starting,

a separate source of current means for supplying the field winding witha redetermined amount of direct current rom the separate source ofcurrent to cause the polarity of the direct current side of theconverter to be in a predetermined direction each time the converter isstarted, and means for rendering the rectifier device and the means forsupplying direct current to the field wind- :m ing ineflective when theconverter has reached su stantially synchronous speed and developed apredetermined polarity.

19. In a starting system for a rotary converter provided with field andarmature windings, in combination, a source of alternating-currentpower, means for starting the converter from the power source, saidfield winding being-directly connected across the converter commutator,means for controlling 4 the direction of flow of the generated currentin the field circuit, means connected to the power source for supplyingthe field winding with unidirectional current in the same direction asthat supplied from' the commutator, and means operable to render boththe direction controlling means and-the current supplying meansineffective after the converter has developed a predetermined polarity.Y m In testimony whereof, I have hereunto subscribed my name this 20thday of May, 1931.

CHARLES P. WEST.

